1. Field of the Invention
This invention relates generally to a method and an apparatus for agitating a bath melted metal to treat the same physically, chemically or metallurgically, such as, for example, by degasifying, desulphurizing or alloying.
2. Description of the Prior Art
In the art of treating a metal, such as for example, an iron, a nonferrous metal or an alloy, in the form of a melted bath thereof, with or without supplying additives thereto, by degasifying, desulphurizing, alloying, and the like, it is essential that the bath of melted metal is agitated as intensely and uniformly as possible. As a method of agitating a bath of melted metal, it is conventionally known to use mechanical agitating means, such as an impeller or a stirrer. However, such mechanical agitating means are generally bound with much of the difficulties caused by the high temperature to which mechanically movable means are usually subject, whereby the cost of the equipment is quite high, while the same usually enjoys a relatively short life span.
Another conventional method of agitating a bath of melted metal is to blow a gas or gases into the bath. The gas blown into the bath forms a number of bubbles which rise through the bath to the surface thereof, and these bubbles agitate the body of the bath while rising therethrough, and particularly they agitate the surface region of the bath as they penetrate the surface layer. In most cases of treating a bath of melted metal, the surface layer of the bath is formed with a treating agent such as a desulphurizer, and therefore, the agitation of the surface layer by bubbles penetrating therethrough is effective to cause the melted metal and the treating agent to contact and mix with each other. In this method, however, it takes much time to have all parts of the body of the bath contacted and mixed with the treating agent floating on the surface region of the melted metal, and the efficiency of treatment is recognized as being relatively low.
As still another conventional method of agitating a bath of melted metal, it is known to generate a natural circulation of the bath by blowing a gas or gases therein. When a gas is blown into a bath of melted metal to form a number of small bubles therein, a portion of the bath, including the bubbles, shows a decreased apparent specific gravity so long as the bubbles remain therein, and therefore, if the gas is continuously blown into a particular portion of the bath, it is possible to form a portion in the bath where the apparent specific gravity is constantly being reduced as compared with the surrounding portions of the bath. Thus, for example, by defining a columnar region in the bath by means of a tubular member 4, as shown in FIG. 1, and blowing a gas into the columnar region at a lower portion thereof through a gas inlet passage 7 having openings 9 to the columnar region, the apparent specific gravity of the columnar region is reduced as compared with that of the surrounding region 2, whereby a natural circulation of the bath into the columnar region through openings in the bottom of the tubular member 4, upward within the tubular member and out through side openings 6 in the upper region of the tubular member for mixing with the surrounding bath portion 2 is generated. However, in this conventional method of generating a natural circulation in the bath, the agitation is still not sufficient, especially when the melted metal is to be treated by being contacted and mixed with a treating agent floated on the surface of the bath, because in this method, the flow of the melted metal generated by the natural circulation is always poured on the same portion of the floated layer of the treating agent, and therefore, all portions of the treating agent forming the floated layer are not effectively brought into contact with the melted metal, thereby resulting in a treating operation of poor efficiency and one requiring much time.